Comparison of pure and hybrid DFT functionals for geometry optimization and calculation of redox potentials for iron nitrosyl complexes with “μ-SCN” bridging ligands

Abstract

AbstractThe geometry and electronic structure of neutral molecules and mono-anions of iron nitrosyl complexes with “µ-SCN” bridging ligands [(¼-SC7H4SN)Fe(NO)2]2 (I) and [(µ-SC2H3N4)Fe(NO)2]2 (II) were studied using the density functional theory: pure functionals BP86, OLYP, OPBE, TPSS, PW91 and hybrid functionals B3LYP, B1B95, B3PW91 along with 6-311++G**//6-31G*. For geometry optimization, the pure functionals are more appropriate than the hybrid functionals. For mono-anions, pure functionals favor the doublet over the quartet state by 8.0–13.9 kcal/ mol, whereas hybrid functionals yield quartet spin state of these anions to be more stable. The redox potentials of complexes I and II have been computed by DFT and compared with experimental results obtained from cyclic voltammetry method. The calculated redox potentials for I and II with pure functionals (especially BP86) are close to the experimental values, whereas those obtained by using hybrid functionals significantly deviate from the experiment.KeywordsDFTPure and hybrid functionalsIron nitrosyl complexesRedox potentials